Transparent thermoplastic material



Patented July 2, i935 umrso STATES [O F E TRANSPARENT THERMOPLASTIC .MATERIAL Samuel Whyte, Redhill, and William Edward Lord. Hayes, England, assignors to'Electric and Musical Industries, Ltd., Hayes, England, a companyof Great Britain No Drawing. Application July 7, 1932, Serial No. 7

621,308. In Great Britain July i931 I I 6 Claims; (oi. 10642) pressing transparent films of cellulosematerial.

onto a paper base which is printed with pictorial, advertising or descriptive matter.

The clear cellulose material forming the playing surface ofsuch records, however, is easily torn upbythe' sharp point of an ordinary steel needle, and these records can only be played satisfactorily ii. a run-in needleis' used, 1. e., one which has had the sharp edge removed by playing on a record made with shellac orother hard introducing mineral fillers into'the material, but,

hitherto, this has" not been possible in the case of pictorial records of the type in question be- "cause of the necessity for maintaining trans-,

parency in the surtacelayer. We have now (118-, covered that certain forms 01' naturally occurring silica can be introduced, into plastic cellulose compositions to give resistance to the tearing action of the needle, without destroying the transparency oi the material when in' a thin layer, as for instance in thickness of 0.005,? to 0.010", which are suitable thiclmess'es for the playing surfaces of records of the type referred to..

We reierparticularly to that form of, absorp- I tive silica known as diatomaceous earth,'deposits of which occur in almost every country in the world, and which comprisethe fossilized remains of microscopic plants or diatomsr Y It is of great importancethat the diatomaceous earth used should be light in color andas free which is then passed between heavy calender rolls ,to form a thin sheet.

as-possible from impurities such as oxides of iron and aluminium, clay, sand, chalk and magnesia. All of these impurities will detract from the transparency of the film. It is also equally. important that the earth should be .as line as possible. We have found that when the flllerparticles do not exceed 0,0l 0millimetre in diameter, it is possible to introduce as much as 30 per cent of it into the cellulose composition without serious loss of transparency'in a film;0.005 to 0.010 inthick- .fness, 5 per cent of-diatomaceous earth of the requisite degree of finenesscontained in a cellulose acetate film 0.020" in thickness was practically invisible. When the, size of the filler particles exceeds 0.020 min. indiameter, the film is rendered 0paque.,-Particle, sizes of 0.010 mm. and 0.020. diameter correspond to sieve meshes of approximately 1200 and600 respectively. It may besaid that; the most desirable varieties of diatomaceous earth are those having a high silica content together with a high absorptivity, and which will pass completely through a hypotheticallOOO mesh sieve.

' It should be understood that under the term ,cellulose compositions", we include organic and inorganic esters of cellulose, examples of which are acetyl, cellulose and nitro-cellulosa-respectively, and also cellulose ethers,-such as, or example, benzyljcellulose and ethyl cellulose.

The cellulose compositions may be prepared by any known processes and may involve the use of volatile solvents such as acetone, dimethyl ketone, alcohol, benzene or the like. They may also contain high, boiling solvents, or plastifler such as camphor, or camphor substitutes, as, for ex-v ample,. triphenyl phosphate, diethyl phthalate, triacetin, alkylatedsulphonamide derivatives of aromatic hydrocarbons, or the like. The manufacture of the material may be carried out by the known processes of masticating, mixing, or kneading with volatile solvents to form a dope or varnish, or a material of a putty-like consistency which may be spread onto the printed paper and dried, or, alternatively, may be spread onto a non-adherent surface, dried, and stripped as a film. 1

The materials may also be worked together with limited quantities of volatile solvents to form a horny mass which may be furthermixed on rollers, pressed into blocksand sliced into sheets of the desired thickness. By other known methods, thesurface films may be prepared according to processes of workingthe materials together on i heated; rolls with or without volatile solvents,

plastifying agents, etc., to form a rubbery mass We have also discovered that diatomaceous earth of the type described may be incorporated ,withvarious synthetic resins which are colorless oronly lightly colored. The same result in regard to transparency is obtained as with the cellulose compositions. For example, a urea-thiourea-formaldehyde resinous condensation product containing a flexibilizer such as glycerine or a glyceryl derivative may be loaded with 30 per cent of diatomaceous earth and worked up into a thin film which is transparent. Other suitable colorless synthetic resins of known type are prepared frorn glycerine and phthalic anhydride, vinyl acetate and vinyl chloride. Mixtures of the above with cellulose compositions may also be employed. 3

Thus, according to the present invention, a transparent film or layer having as basis a material such as ,a cellulose derivative or asynthetic resin contains a filler consisting of a naturally occurring silica such as diatomaceous earth.

By way of example, two processes for'the prep aration of transparent films for sound records will now be described.

In Process I, a cellulose derivative is employed as the basic material while in Process II, a synthetic' resin is used.

Process I .-40 parts of powdered, low'viscosity cellulose acetate, preferably of 40 mesh fineness, are mixed with 30 parts of finely divided 1,000 mesh) diatomaceous earth, together with 4 parts of triphenyl phosphate, 12 parts of diethyl phthalate and 13 parts of toluene sulphonethylamide. It should be understood that any other known plastifiers for cellulose acetate may be used providing they are capable of yielding lightcolored acetate films.

The selection of plastifier is not vital to the transparency of the film, but it is obviously advantageous to avoid those plaistifiers known to produce dark colored products insofar as a dark transparent film will not give the same true value to the printed colors as a colorless film.

The mixed materials are heated and mixed either in a mastioating machine or on rollers, preferably in the presence of a'small quantity of acetone or other volatile solvent until a plastic mass is produced which is completely freefrom white specks of cellulose acetate. The presence of a small amount of solvent enables plastification to be carried out at a relatively low temperature such as F. During the process of mix-- ing on the. rolls, the solvent is slowly volatilized, the plastic mass gradually becoming stiffer.

At a suitable stage of the process, the plastic material is withdrawn from the mixer and passed between heavy calender rolls to formthin sheets of from 0.005" to 0.010" in thickness.

The sheets are hung for several days in a heated, ventilated chamber at a temperature of approximately 100 F. for the purpose of eliminating the last traces of solvent. Discs of suitable diameter (which may appear translucent at this stage) are cut from the sheets and are then ready for combining with the printed paper core layer to form the completed record:

Either a single thickness of paper printed on each side may be used or, if more convenient, two paper discs, each printed on one side, may be joined on their unprinted sides by means of a thin layer of shellac or other adhesive, or the record can be built up by the use of a plurality of cemented layers of paper to any desired thickness.

The layers are assembled between steam-heated matrices or pressing plates in a hydraulic press, the transparent film being, of course, immediately adjacent to the heated plates. Pressure is applied, the layers are amalgamated, and the sound impression is formed. Finally, the record is cooled before releasing the pressure.

During the pressing process, the surface films are rendered more transparent and become more flexible. The printed design on the paper beneath the surface then stands outclearly.

Instead of low. viscosity cellulose acetate, medium or high viscosity cellulose acetates may be used, or benzyl cellulose or any other suitable cellulose derivative.

Process IL-A resin syrup is first prepared by condensing in known manner urea or thiourea with formaldehyde, the water content of the syrup being subsequently reduced to approximately 10 per cent by evaporation. Mixtures of urea and thiourea may also be employed. The viscous syrup is used in this form as a base for the surface composition, and in accordance with-the invention may be incorporated with diatomaceous earth and fiexibilized in the following proportions:-

Parts by weight Urea or thiourea resin syrup (10% water) 50 Diethylene glycol (or other glyceryl derivative) 25 Diatomaceous earth 25 A small amount of oxalic acid (for example 1-2%, reckoned on the resin content) may be added to accelerate the subsequent hardening of the surface film during the pressing operation. If preferred, other organic acids, such, for example, as salicylic acid, tartaric acid, or citric acid maybe employed as accelerators.

The filling agent is milled with the mixture of ethylene glycol and resin syrup, alcohol being added at discretion to produce a consistency suitable for spreading. A dry coating of suitable thickness is obtained by applying to the printed paper support a varnish coat .010"-.015" in thickness, or, preferably, by applying a succession of thinner coats, until the desired thickness is reached. After having been coated, the varnished printed paper discs or sheets are dried for 1 hour at 65 C. and finally impressed with the sound grooves by pressing between heated matrices at a temperature of 280-310 F. It has been found that a complete cure of the resin composition is effected in 15-30 seconds when a pressure of approximately 1500 lbs. per square inch and a temperature of 300 F. are employed.

In either of the two processes described above, if it is desired to enclose completely or to seal the edges of the paper discs, the latter should be cut smaller in diameter than the surfaces, as for example 9% for a record having a finished overall diameter of 9%", so that the two overlapping clear films will be joined together at the edge by the pressure of the rings holding the matrices.

In the foregoing examples, the invention has been described as adapted specifically to the production'of transparent films for sound records, but it will be clear that such films will find application as surface coatings in a variety of circumstances in which resistance to wear is an essential property of the coating.

Many modifications of the processes hereinbefore described will be apparent to one skilled in the art, and it is to be understood that the invention is not to be limited to the particular ex amples given but'only insofar as it is defined by the appended claims.

We claim as our invention 1. A composition of matter comprising' a thermoplastic material which is transparent in thin sheet form and which has incorporated therein a filler of diatornaceous earth substantially free from coloring oxides, said filler being of a particle size insuflicient to substantially alter the transparency thereof and in an amount sufficient to impart wear resistance to said material under the action of a phonograph needle.

2.- A composition of matter according to claim 1 wherein the thermoplastic material comprises a cellulose derivative and wherein the weight of the filler is substantially three-quarters that of the cellulose derivative. v

3. A composition of matter according to claim 1 wherein the thermoplastic material comprises a synthetic resin and wherein the weight of the filler is substantially one-half that of the resin.

4. The method of forming phonograph records which comprises mixing with a material adapted to have sound grooves formed therein and which is transparent when in thin sheet form diatomaceous earth substantially free from coloring oxides and reduced to a particle size such that no loss of transparency in said material will result therefrom, the diatomaceous earth being man I amount sufficient to impart wear resistance to the record. s

I 5. The method of forming phonograph records which comprises mixing with a reactive synthetic resin which cures to transparent form in thin sheets and which, is adapted to have sound grooves formed therein, a filler of diatomaceous earth substantially free from coloring oxides and reduced to a particle size such that no loss of transparency in said resin will result therefrom, the diatomaceous earth being in an amount sufilcient to impart wear resistance to the record.

6. The invention set forth in claim 5 characterized in that the indices of refraction of the diatomaceous earth and the cured resin are substantially the same.

SAMUEL WHYTE. WILLIAM EDWARD LORD. 

